1. Field of the Disclosure
This disclosure relates to free radical and controlled radical polymerization processes of atom or group transfer radical polymerization, and to (co)polymers prepared therefrom.
2. Discussion of the Background Art
Atom transfer radical polymerization (“ATRP”) is considered to be one of the most successul controlled radical polymerizations (“CRP”). A CRP process is a process performed under controlled polymerization conditions with chain growth proceeding via a radical mechanism, such as, but not limited to, ATRP, stable free radical polymerization, (“SFRP”), nitroxide mediated polymerization, (“NMP”), reversible addition-fragmentation transfer, (“RAFT”) or degenerative transfer systems.
A feature of CRP is the creation of an equilibrium between active polymer chain and dormant polymer chain. In certain embodiments, it may be preferable if a majority of polymer chains are present as dormant polymer chains. The equilibrium between the active and dormant chains typically provides for more controlled chain growth relative to conventional free radical polymerization. CRP processes are capable of producing mere uniform polymers; however, the active propagating chain may react in termination reactions resulting in higher polydispersities. Therefore, typically, to minimize termination reactions, the instantaneous concentration of active propagating species is maintained at a low concentration.
In CRP, the ability to maintain or adjust the equilibrium between active and dormant species and quantitative initiation early in the polymerization process allows, under appropriate conditions, the capability for synthesis of polymers with special architecture and functionality. In addition, if desired, the overall rate of monomer conversion may occur at rates equivalent to uncontrolled polymerization. Controlled polymerization process may be used to prepare polymers having a degree of polymerization that may be approximated from the ratio of the amount of consumed monomer to the initiator, a polydispersity close to a Poisson distribution and functionalized chain ends.
ATRP is the most often used CRP technique with a significant commercial potential for many specialty materials including coatings, sealants, adhesives, dispersants but also materials for health and beauty products, electronics and biomedical applications. The most frequently used ATRP is based on a simple reversible halogen atom transfer catalyzed by redox active transition metal compounds.
Certain advantages of an ATRP are as follows, many commercially available inexpensive initiators, catalysts and ligands may be used; many polymers produced by ATRP allow facile functionalization or transformation of the end groups by replacing terminal halogens with azides, amines, phosphines and other functionalities via nucleophilic substitution, radical addition or other radical combination reactions; an abundance of polymerizable monomers are available; allows production of macromolecules with complex topology such as stars, combs and dendrimers, coupled with the ability to control composition (block, gradient, periodic copolymers) and even control of polymer tacticity; and allows a simple reaction which may be carried out in bulk, or in the presence of organic solvents or in water under homogeneous or heterogeneous conditions, in ionic liquids, and CO2.
Rising economies across the globe are increasing demand for diene-based polymers, especially those commonly used in the automotive industry. In addition to the automotive industry, the market for diene-based polymers is bolstered by expanded applications for these materials in adhesives and as substitutes for metal and glass, and also engineered plastics. The industry is continuously looking for ways of gaining a competitive advantage and reducing production costs.
Current diene industrial polymerization is carried out using water sensitive anionic techniques. Carrying out the diene polymerization using free radical methodologies would greatly simplify the process and give new structures. For example, if diene polymerization could be carried out by ATRP including block polymer synthesis, it would be possible to bypass all the stringent purification procedures associated with anionic polymerizations. It would also be possible to make block copolymers and other structures not accessible via anionic polymerization.
The industrial manufacture of polymers of conjugated 1,3-dienes such as butadiene (BD), isoprene (ISO) and chloroprene ranks in the billions of pounds/year, thus rendering their synthesis very relevant. However, while the large scale production of adhesives, rubbers, coatings and high impact materials based on random copolymers of dienes with AN or Sty can take advantage of radical emulsion polymerizations, the industrial synthesis of the corresponding well-defined thermoplastic elastomer block copolymers is still carried out only by expensive, air and water sensitive, anionic or coordination polymerization techniques which require stringent conditions, and limit the range of initiator/chain end functionalities. As such, less demanding, inexpensive and water tolerant, reversible deactivation controlled radical polymerizations (RDCRPs), would be highly beneficial. However, the radical polymerization of dienes is plagued by a set of problems including a low boiling point (bpBD=−4.4° C., bpISO=34° C.), one of the lowest rate constant of propagation (kp) of all monomers, Diels Alder dimerization, as well as a weak, side reactions prone, allylic chain end in CRPs.
Accordingly, the low kp and low bp prompt the need for high temperature (T>50° C.), pressurized metal reactors. Experimentally, this presents a problem for reaction optimization, as by contrast to trivial MMA or Sty CRPs, easily sampled from Schlenk tubes, diene kinetics involve cumbersome one data point experiment sets (i.e. 4-5 polymerizations for a kinetic plot).
As such, while a vast body of literature exists on the CRP of non-gaseous monomers, only very few papers address dienes, and predominantly, isoprene. Notable examples include CRPs mediated by nitroxides, RAFT reagents, organo-Te derivatives, and to a much smaller extent by iodine degenerative transfer telomerization.
Clearly, the widely popular, Cu-mediated ATRP would greatly benefit the industrial synthesis of dienes-based polymers, especially in view of the low cost and commercial availability of all reagents, its catalytic nature, water tolerance, and the great flexibility in fine-tuning the polymerization by the rational selection of the alkyl halide initiator, metal/ligand combination and of other reaction parameters. Yet, after almost 20 years since the original reports, and over 10,000 ATRP papers later, while the in-depth mechanistic understanding has made considerable advances, enabling ATRP optimization to excellent control over styrene and (meth)acrylates, its extension to VAc, VDF, ethylene or dienes has proven troublesome/challenging. Indeed, the results of the very few attempts at diene ATRP, are at best disappointing, and to date, there is no convincing evidence of the ATRP of dienes, no reliable diene ATRP procedures, or a quantitative understanding of the specifics of diene ATRP including kinetics, mechanism, catalyst, ligand or solvent effects and of the complex interplay of various rates, rate constants and especially of side reactions.
Thus, there is a need to develop reliable diene ATRP procedures. Further, there is a need to simplify and reduce costs associated with current diene industrial polymerization that uses water sensitive anionic techniques.
The present disclosure also provides many additional advantages, which shall become apparent as described below.